The invention results from problems and disadvantages associated with prior art concerning placement of remedial seals in annuli in a well after completion and during the operating phase thereof.
A well is normally composed of several casing strings of different diameters, and these are arranged within each other having annuli therebetween. The strings, which have successively decreasing diameters, extend down to different depths in the well. A casing string of this type may be fixedly cemented, wholly or partially, in its well bore. Alternatively, the casing string may be uncemented in the well bore, i.e. a so-called open hole completion. The latter variant is common in a reservoir section of a hydrocarbon well. In order to establish a flow connection with surrounding rocks, the casing may be provided with openings, for example holes or slots, prior to installation in the well, or the pipe may be perforated after installation. In a production well, this pipe is described as production tubing. The casing may also be provided with one or more filters, for example sand screens, in order to filter out formation particles from a formation fluid before it flows into the well. Furthermore, the casing may be provided with a so-called gravel pack, for example sand or similar, between said filters and the surrounding rocks.
In addition, various well packers are used to isolate zones, for example one or more reservoir zones, along a well pipe, i.e. a casing with or without said filter, in a well. Packers of this type are normally placed on the outside of the specific well pipe and before it is conveyed into the well. This type of packer is commonly referred to as an external casing packer—“ECP”. When the well pipe has been conveyed and positioned at the corrected location in the well, the packer(s) is/are activated in the annulus around the well pipe and is/are forced against surrounding rocks or a surrounding well pipe. Activation of such a packer may be carried out hydraulically, mechanically or by means of a swell packer that will expand upon contact with, for example, oil in the well. Packer setting techniques of this type constitute prior art.
During the post-completion phase of a well, particularly in connection with recovery of hydrocarbons from a reservoir, production-related problems or conditions may arise that necessitate or generate a need for installing one or more further annulus packers in the well. Installation of such remedial annulus packers may form part of an appropriate production management and reservoir drainage strategy, or the installation may be carried out in order to remedy an acute situation in the well. Accordingly, a need may exist for isolating one or more zones both in a production well and in an injection well, and the need may arise at any time throughout the lifetime of a well. The need will normally be greatest in horizontal wells and highly deviated wells. Deficient or failing zone isolation may restrain or prevent various efforts to stimulate the recovery from a well, which may reduce the recovery factor and profitability of the well and/or the reservoir. Insufficient zone isolation may also lead to unfortunate and/or dangerous conditions in the well.
The following examples point out some well conditions in which effective and selective annulus sealing may be of great significance to the performance of a well:                Blocking of undesirable fluid flows, for example a water flow, from specific zones/intervals and into a production well, such as undesirable fluid flows from faults, fractures and highly permeable regions of surrounding rocks;        Blocking of undesirable fluid flows to so-called “thief-zones” in an injection well, such as undesirable fluid flows to faults, fractures and highly permeable regions of surrounding rocks; and        Selective placement of well treatment chemicals, including scale inhibitors and stimulation chemicals, in individual zones of a production well or injection well.        